The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A typical modern multiple speed automatic transmission includes a plurality of planetary gear assemblies and selectively engaged friction clutches and brakes that achieve a plurality of forward speeds or gear ratios and reverse.
Increasingly demanding economic, performance and efficiency goals continue to encourage automatic transmission research and development. A result of this effort has been a steady increase in the number of available forward speeds or gear ratios in an automatic transmission.
Whereas three or four speed automatic transmissions were once commonplace and considered to provide sufficient operating flexibility and performance, the industry and consumer preference has moved to five, six and eight speed automatic transmissions.
In such transmissions, the elements of a plurality of planetary gear assemblies are (1) connected by permanent coupling members, (2) selectively connected by friction clutches or (3) selectively grounded by brakes. Specific combinations of the clutches and brakes are engaged or activated in sequence to provide a predetermined sequence of numerically related gear ratios and thus output speeds and torques.
Because they so closely match the power and torque outputs of an engine to vehicle speed and load, five, six and eight speed automatic transmissions provide significant performance enhancements and fuel consumption reduction. Nonetheless, such transmissions are known to have drawbacks. A pair of known and related drawbacks are complexity and cost. A corollary to such complexity is frictional loss. Each of the torque transmitting devices, namely, the clutches and brakes, contributes to frictional losses, referred to as spin losses, when they are not engaged. Three primary factors influence spin losses: the total number of clutches and brakes, the size or torque capacity of the clutch or brake and the instantaneous speed difference between the input and output of the clutch or brake. Frictional losses, of course, also increase with increasing transmission complexity.
Because of their benefits and in spite of their drawbacks, there is ongoing and increasing demand for automatic transmissions having eight or more forward gears or speed ratios. The present invention provides an automatic transmission having eight, nine, eleven or thirteen forward speeds or gear ratios and one which exhibits reduced frictional losses.